1. Field of Invention
The present invention relates to the field of flow control. More specifically, the invention relates to a device and method for controlling the flow of fluids in a wellbore that, in one embodiment, provides for full tubing flow.
2. Related Art
The economic climate of the petroleum industry demands that oil companies continually improve their recovery systems to produce oil and gas more efficiently and economically from sources that are continually more difficult to exploit and without increasing the cost to the consumer. One successful technique currently employed is the drilling of horizontal, deviated, and multilateral wells, in which a number of deviated wells are drilled from a main borehole. In such wells, and in standard vertical wells, the well may pass through various hydrocarbon bearing zones or may extend through a single zone for a long distance. One manner to increase the production of the well, therefore, is to perforate the well in a number of different locations, either in the same hydrocarbon bearing zone or in different hydrocarbon bearing zones, and thereby increase the flow of hydrocarbons into the well.
One problem associated with producing from a well in this manner relates to the control of the flow of fluids from the well and to the management of the reservoir. For example, in a well producing from a number of separate zones, or laterals in a multilateral well, in which one zone has a higher pressure than another zone, the higher pressure zone may produce into the lower pressure zone rather than to the surface. Similarly, in a horizontal well that extends through a single zone, perforations near the "heel" of the well--nearer the surface--may begin to produce water before those perforations near the "toe" of the well. The production of water near the heel reduces the overall production from the well. Likewise, gas coning may reduce the overall production from the well.
A manner of alleviating this problem is to insert a production tubing into the well, isolate each of the perforations or laterals with packers, and control the flow of fluids into or through the tubing. However, typical flow control systems provide for either on or off flow control with no provision for throttling of the flow. To fully control the reservoir and flow as needed to alleviate the above described problem, the flow must be throttled. A number of devices have been developed or suggested to provide this throttling although each has certain drawbacks. Note that throttling may also be desired in wells having a single perforated production zone.
Specifically, the prior devices are typically either wireline retrievable valves, such as those that are set within the side pocket of a mandrel, or tubing retrievable valves that are affixed to the tubing string. An example of a wireline retrievable valve is shown in U.S. patent application Ser. No. 08/912,150 (U.S. Pat. No. 6,070,608 ) by Ronald E. Pringle entitled Variable Orifice Gas Lift Valve for High Flow Rates with Detachable Power Source and Method of Using Same that was filed Aug. 15, 1997 and which is hereby incorporated herein by reference. The variable orifice valve shown in that application is selectively positionable in the offset bore of a side pocket mandrel and provides for variable flow control of fluids into the tubing. The wireline retrievable valve has the advantage of retrieval and repair while providing effective flow control into the tubing without restricting the production bore. However, one drawback associated with the current wireline retrievable-type valves is that the valves cannot attain "full bore flow." An important consideration in developing a flow control system pertains to the size of the restriction created into the tubing. It is desirable to have full bore flow meaning that the flow area through the valve when fully open should be at least about as large as the flow area of the tubing so that the full capacity of the tubing may be used for production. Therefore, a system that provides full bore flow through the valve is desired.
A typical tubing retrievable valve is the standard "sliding sleeve" valve, although other types of valves such as ball valves, flapper valves, and the like may also be used. In a sliding sleeve valve, a sleeve having orifices radially therethrough is positioned in the tubing. The sleeve is movable between an open position, in which the sleeve orifices are aligned with orifices extending through the wall of the tubing to allow flow into the tubing, and a closed position, in which the orifices are not aligned and fluid cannot flow into the tubing. Elastomeric seals extending the full circumference of the sleeve and located at the top of the sleeve and the bottom of the sleeve provide the desired sealing between the sleeve and the tubing. Due to the presence of the elastomeric seals, reliability may be an issue if the sleeve valve is left downhole for a long period of time because of exposure to caustic fluids. Further, because the valves are tubing retrievable, any failure of the valve can only be repaired by pulling the tubing from the well and replacing or repairing the valve. However, such a retrieval operation is generally impractical and always costly. Therefore, the typical manner of correcting failures in tubing retrievable valves is to "pack-off" the flow passageway with a bridge plug. Packing off the flow passageway, though, creates a restriction in the production bore and limits production. Also, the bridge plug must be removed each time the well is entered for service. Thus, although the tubing retrievable valves have the advantage of full bore flow, this advantage is often outweighed by the risk of failure.
Remote actuators for the sleeve valves have recently been developed to overcome certain other difficulties often encountered with operating the valves in horizontal wells, highly deviated wells, and subsea wells using slickline or coil tubing to actuate the valve. The remote actuators are positioned in the well proximal the valve to control the throttle position of the sleeve.
However, after a sleeve valve has been exposed to a wellbore environment for some time, the sleeve may be stuck or rendered more difficult to operate due to corrosion and debris. Additionally, the hydraulic seals of the sleeve add substantial drag to movement of the sleeve valve, rendering its operation even more difficult. Sleeve valves may require relatively large forces to overcome the drag from hydraulic seals in the valve, particularly when the sleeve valve is exposed to high pressure and corrosion. In addition, a sleeve valve may require a relatively long stroke to move between a fully open position and a fully closed position. As a result of the relatively large forces and long strokes employed to actuate a sleeve valve, an actuator employed to open and close the valve may need to be relatively high powered. Providing such high power may require a large actuator, sophisticated electronic circuitry, and relatively large diameter electrical cables, run from the surface to the valve actuator mechanism.
A solution aimed at alleviating these problems associated with the sliding sleeves is shown in application Ser. No. 09/243,401, by David L. Malone, entitled Valves for Use in Wells, filed Feb. 1, 1999 which is hereby incorporated herein by reference. In particular, that solution is to use a sophisticated valve design that has valve covers that provide a seal around the periphery of the cover and the orifice through the tubing. The valve covers are sized in accordance with the size of the orifice. In this way, the surface of contact between the cover and the tubing, or seat, is much less than that encountered with a sliding sleeve and the stroke length is decreased. Additionally, the valve uses low coefficient of friction material, such as a polycrystalline diamond coating, to facilitate sliding and incorporates a self cleaning feature aimed at removing built up debris that tends to impede valve movement.
The valves may be packaged and used in a number of ways to control the flow of fluid into the tubing (as well as through the tubing and other applications). One embodiment of the present invention is directed at a preferred manner of incorporating these valves into a workable flow control system. Note, however, that other valves may also be useable in the present system.
Despite the features of the prior art, there remains a need for a flow control system that may be repaired or packed-off without impeding the flow through the tubing, that provides for full bore flow, that reduces the power requirements for operation over previous designs, that is adaptable to the requirements of the particular well, and that provides an efficient, reliable, erosion-resistant system that can withstand the caustic environment of a well bore.